Kotlin Notes for Professionals – PDF Download

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All Kotlin programs start at the main function. Here is an example of a simple Kotlin “Hello World” program:

Place the above code into a file named Main.kt (this filename is entirely arbitrary)
When targeting the JVM, the function will be compiled as a static method in a class with a name derived from the filename. In the above example, the main class to run would be my.program.MainKt.

To change the name of the class that contains top-level functions for a particular file, place the following annotation at the top of the file above the package statement: @file:JvmName(“MyApp”)

In this example, the main class to run would now be my.program.MyApp. See also:

Package level functions including @JvmName annotation. Annotation use-site targets

Section 1.2: Hello World using a Companion Object

Similar to using an Object Declaration, you can define the main function of a Kotlin program using a Companion Object of a class.

package my.program

un main(args: Array) { println(“Hello, world!”)